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1 pipe steam system- 2 zones, 1 gets hot much faster then the other.

I have a 1 pipe steam system with 2 mains (Crown BSI103) just installed and I am having trouble with 1 main not heating up as fast as the other. If you look at the picture (Near boiler piping) you see the 1 pipe goes up from the header into a oversized tee and one main goes straight up (no issue with heat) but the main that is off the tee takes twice as long to get hot. should both mains be right off the header separately or is that over sized tee ok? Seems like the steam wants to go up much faster then turn 90 degrees. I've asked the contractor to re-pipe it but they seem to think its a venting issue. I believe it isnt a venting issue as all vents are new (including master vents) and they all seem to be working fine. all the radiators on the main that goes strait up get warm pretty much at the same time and the ones off the tee eventually get warm at the same time but by the time that happens the 1st side to too warm.
Honeywell pressure trol was set st 3 PSI main and 1 Diff, they adjusted to 1 1/2 ish main and slightly below 1 Diff. any thoughts on pressure?


  • Jamie Hall
    Jamie Hall Member Posts: 21,547
    Oh dear. I could make several comments, but in direct answer to your question, yes, both mains should have come directly off the header (which should have been bigger... and had both risers... but oh well). Whether that would help the unevenness, however, I wouldn't care to say. How is the venting on the twon mains?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Long Beach Ed
  • gfrbrookline
    gfrbrookline Member Posts: 727
    Call your contractor back and make him/her install the near boiler piping to the manufacturers specs. The piping is all wrong and that is why you have the problems you are experiencing. Your contractor either cut corners or has no experience with steam, every steam boiler comes with instructions on near boiler piping that needs to be followed. Do not pay the contractor until they fix the piping.
  • TommyMeBoy
    TommyMeBoy Member Posts: 4
    The header is a kit from Crown for the boiler, are you talking about the tee and 2 mains?
  • mattmia2
    mattmia2 Member Posts: 8,435
    Missed it by that much.

    Looks like the fittings we had on the truck job.
  • mattmia2
    mattmia2 Member Posts: 8,435
    edited November 2022
    I think the tee is very much your problem. I seem to recall a similar thread a couple years ago when someone that knows steam far better than i said that the steam prefers one direction over the other with a tee like that.

    Also if that horizontal piece off the tee isn't level or pitched toward the riser, it will hold water there and stop the steam from taking the branch until it is heated by the steam.
  • KC_Jones
    KC_Jones Member Posts: 5,431
    Yes the mains should be connected into the header individually, I attached a mark up for reference. What can happen with the setup you have there is the steam will favor going through the run of the tee instead of the take off of the tee.

    In addition to get balance you would need to look at the venting you have at the ends of the mains, that is what controls how fast the mains can fill relative to one another, that is once the piping is correct at the boiler.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • TommyMeBoy
    TommyMeBoy Member Posts: 4
    Everyone is pretty much confirming my thoughts. 
    When you connect the two risers, do you need the elbows above the header or do they connect straight in?
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,144
    edited November 2022
    You can probably get this to work better, or maybe even fine without piping it correctly.

    You'd have to slow the venting of the radiators on the run of the tee, which would force steam to favor the bull of the tee at least to get distribution started.

    This, of course would have a negative effect on distribution efficiency, for which you would pay over the next forty years. But you won't have to repipe the header. Silly, because this would have been easy to do properly.
    JUGHNE Member Posts: 10,798
    So that is the header kit for that size of boiler? Only 2"?

    It looks as if your guy has as much work and money invested in the wrong fittings as he would of had in the right ones.

    And don't let him use that oversized tee in the header for the second riser.

    It will have a perpetual pool of water in the bottom of it and give you hammer.
  • Danny Scully
    Danny Scully Member Posts: 1,407
    edited November 2022
    The boiler is likely piped to manufacturers specifications, especially if they used the kit crown offers. Steam does not feed into the Bull of the tee, so technically, there is no issue there (assuming the connected radiation isn’t larger than 2” can handle). It isn’t how I would have done it at all, but that really isn’t the point. I do believe this to be a venting issue. It seems like the slower main should be vented faster, and/or the faster main should be vented slower. Finally, that pressuretrol is subtractive so it should be set to 2 for the main and 1.5 for the diff. 
  • TommyMeBoy
    TommyMeBoy Member Posts: 4
    you say is does not feed into the bill of the tee, wouldn’t that mean it’s not going to work? 
    Installation section says to set the pressuretrol to .5 Main and 1 1/2 diff. 

    I do get a bit of water hammer until the bull of the tee gets hot which leads me to believe what jughne posted about water gathering there. 

  • Danny Scully
    Danny Scully Member Posts: 1,407
    edited November 2022
    If steam feeds into the Bull of a tee, it’s called a bullheaded tee and this is incorrect. That is not what is happening on your install. The steam is feeding into the run of the tee, which is correct. There is nowhere for water to gather in theory, as it would simply drain back down into the header.

    Did the installer skim the boiler? 

    That specific pressuretrol is subtractive, so 2 would be the main (what pressure it’s off at) and 1.5 would be the diff (2 - 1.5 = .5, what pressure it’s back on at). The manual is likely referring to an additive pressuretrol, where the cut in is .5 and the diff is 1.5 (.5 + 1.5 = 2, what the pressure cuts out at). You do not have this pressuretrol.

    Most importantly, how did you size all the radiator vents and the main vents?